"If the containment at the nuclear power plant damaged by Japan's devastating earthquake fails, a potential radiation plume from a full core meltdown could reach Tokyo, a U.S. scientists' organization said on Tuesday.

Japan faces a potential catastrophe after a stricken nuclear power plant exploded and sent low levels of radiation floating toward Tokyo, prompting some people to flee the capital and others to stock up on essential supplies.

The Union of Concerned Scientists also said a 'jerry-rigged' cooling system at the Japanese plant would be hard to maintain if all workers there were evacuated."